Japanese Patent Application Laid-Open No. 2006-220020 discloses a technology in which to warm up a catalyst, ignition timing is retarded and the air-fuel ratio of the air-fuel mixture is changed alternately between lean and rich.
Japanese Patent Application Laid-Open No. 9-88663 discloses a technology in which the temperature of a catalyst is raised by operating one or some of the cylinders of an internal combustion engine at a lean air-fuel ratio and operating the other cylinders at a rich air-fuel ratio. This publication also discloses a technology in which when the temperature of the catalyst is lower than a specific temperature (or a temperature at which oxidation reaction of CO in the catalyst is promoted), execution of the above-described control is disabled.
Japanese Patent Application Laid-Open No. 11-257062 discloses a technology in which to raise the temperature of a catalyst in an exhaust gas purification apparatus for an internal combustion engine having an afterburner provided upstream of the catalyst, the internal combustion engine is operated at a rich air-fuel ratio, and secondary air is supplied to the afterburner.
Japanese Patent Application Laid-Open No. 2000-240547 discloses a technology in which when a spark ignition internal combustion engine is cold-started, ignition timing is advanced to be earlier than MBT, whereby the quantity of heat that cooling water receives is increased.